The present invention relates to a water supply system for a fuel cell, for supplying compressed air having an ideal humidity for the fuel cell.
FIG. 8 shows a known screw-type air compressor.
In this compressor, water flowing in from a water tank 104 is pressurized by a water pump 105, and water is mixed from water supply valve 106 into an intake duct 102 positioned upstream of a screw-type air compressor 101, having a reduced leakage of compressed air at gaps in the screw within the air compressor 101, so that the volumetric efficiency is improved, wasteful air compression is reduced, and the compression work due to latent heat of water vaporization is reduced, whereby the adiabatic compression efficiency is improved.
However, leakage paths of the air compressor 101 are sealed, and a large quantity of water is supplied to improve the adiabatic compression efficiency.
In application to a fuel cell system, therefore, water flows directly into the fuel cell, causing condensation due to an internal temperature of the fuel cell, and water can collect in air flow paths within the fuel cell, thereby interfering with the flow of air and reducing the generating efficiency of electrical power of the fuel cell.
The present invention is made with such points in view. It therefore is an object of the invention to provide a water supply system for a fuel cell, which achieves not only highly precise control of humidity, but also the maximum possible electrical power generating efficiency.
An aspect of the present invention to achieve the object is a water supply system for a fuel cell, comprising a water supply valve responsible for a supply quantity of water to be injected from a water tank into an air intake path, a compressor compressing air taken from the air intake path after the water injection, a cooler cooling compressed air delivered from the compressor to supply cooled air to the fuel cell, a set of detectors detecting a flow rate, a pressure and a temperature of compressed air to be supplied to the fuel cell, a water quantity calculator calculating a necessary water quantity for the fuel cell based on a detected flow rate, pressure, and temperature of the compressed air to be supplied to the fuel cell, and a water quantity controller controlling the water supply valve to supply the necessary water quantity.
According to this aspect, a quantity of water to be injected to the air intake path from the water tank is supplied through a water supply valve, air is taken in from the intake path and compressed after water injection, air delivered from the compressor is cooled, and the cooled air is supplied to the fuel cell, an ideally demanded quantity of water for the fuel cell is calculated based on a detected flow rate, pressure, and temperature of compressed air to be supplied to the fuel cell, and the water supply valve is controlled so as to achieve this quantity of water, thereby achieving highly precise humidity control and also achieving the maximum possible electrical generating efficiency.